1. Field of the Invention
The present invention relates to an apparatus for subjecting a semiconductor substrate to a washing process before a vapor-phase growth film forming step, a diffusion step, etc., of a wafer process in the manufacture of a semiconductor device.
2. Description of the Related Art
FIG. 1 is a view diagrammatically showing a conventional wafer washing apparatus.
A wafer 50, an object of washing, is placed on a wafer support base 58 rotationally driven by an external motor 57. The wafer 50, together with a wafer support base 58, is arranged, in a hermetically sealed state, in a chamber 51 for washing with a chemicals liquid.
Within the chamber 51 above, a vapor supply means 56 is located above the wafer 50. The vapor supply means 56 comprises a substrate washing process bath 53 equipped with an inlet 52 for supplying a chemicals liquid (a hydrofluoric acid, HF), a hot plate 54 for heating the washing process bath, and a vapor supply nozzle section 55.
The washing process chamber 51 is equipped in an upper zone with an inlet 59 for supplying an inert gas, such as an N.sub.2 gas, and in a lower zone with a discharge outlet 60.
A water washing/drying chamber 61 is provided in a side-by-side relation to the washing process chamber 51. A water washing process bath 62 is provided in the washing/drying chamber 61 and has a wafer support base 64 mounted therein. The wafer support base 64 is rotationally driven by an external motor 63. A pure water supply nozzle 65, a water discharge outlet 66 and exhaust outlet 67 are provided in the washing/drying chamber 61.
FIG. 2 shows a wafer 50 comprising a semiconductor substrate 50a, an insulating film 50b formed on the semiconductor substrate 50a and a metal wire 50c formed on the insulating film 50b.
When the wafer 50 is to be washed in the above-mentioned apparatus, the wafer is placed in the washing process chamber 51 and an HF vapor is introduced into the chamber 51 placed in a hermetically sealed state. The wafer 50 is exposed to the HF vapor to allow it to be treated with such chemicals vapor.
In the case where metal particles are left on the wafer surface in the previous chemicals-washing step, such metal particles cannot be removed from the wafer surface simply by supplying the HF vapor to the surface of the wafer. In order to remove the metal particles or a hydrofluoric acid HF adsorbed in or on the wafer surface, the wafer 50 which has been processed with the chemicals vapor is conveyed into the washing/drying chamber 61 where it is washed with pure water. There, the water is dried while the wafer is rotated.
It is possible to, instead of supplying the HF vapor, supply a mixture of an HF gas and water vapor.
In the above-mentioned conventional wafer washing apparatus, the two chambers 51 and 61 are prepared, that is, the chamber 51 for an HF process and the chamber 61 for water-washing and drying. This takes up a greater mount space. In addition to this drawback, the apparatus also encounters a possibility of exposing the wafer 50 to an outer atmosphere on conveyance from the HF process chamber 51 to the wafer washing/drying chamber 61 so that the wafer is contaminated with an organic matter such as carbon, dust, etc.
In the case where a wafer having a grooved pattern on its surface, such as a DRAM wafer having a trench capacitor as, for example, a memory cell's capacitor, is to be washed, a gas or vapor is readily forced into the grooves of the wafer. In the case where such a grooved surface of the wafer is hydrophobic, pure water is hard to penetrate into the grooved surface during washing and it becomes difficult to replace a trapped gas or vapor in the grooves or trenches with the pure water.
There is a tendency that, with an increase in an element's capacity at a DRAM chip area of the DRAM wafer, the trench of the trench capacitor becomes smaller in its opening size and becomes deeper and that it becomes difficult to, at a washing process, wash the trench with pure water.